Answer: C. 12.5
Step-by-step explanation:
Given : A manufacturer of new light bulbs claims the average lifetime of its long-life bulb is more than 4000 hours.
Population mean : [tex]\mu=4000[/tex]
Sample size : n= 100
Sample mean : [tex]\overline[x}=4500[/tex]
Standard deviation: [tex]s=400[/tex]
The value of test-statistic is given by :-
[tex]z=\dfrac{\overline{x}-\mu}{\dfrac{s}{\sqrt{n}}}\\\\\Rightarrow\ z=\dfrac{4500-4000}{\dfrac{400}{\sqrt{100}}}\\\\\Rightarrow\ z= 12.5[/tex]
Hence, the value of the test statistic for this problem is 12.5.
